The present invention relates to an ultrasonic detector that detects whether an ultrasonically conductive medium such as a liquid is present in a container, the detector being field-adjustable to allow an operator in the field to adjust the detector without the need to utilize an oscilloscope or another electrical sensing device.
Conventional ultrasonic detectors may be used to detect the presence or absence of liquid in a container, such as a pipe for example. When used, such a detector is attached to the exterior wall of a pipe and senses whether liquid is present or absent in the pipe at the point of attachment.
The detector operates by transmitting a burst of energy through the pipe wall to which the detector is attached towards the opposite pipe wall. The burst of energy has a frequency such that the burst is greatly attenuated when it travels through air or another gas, but not greatly attenuated when it travels through liquid. The detector senses whether an echo of the transmitted burst of energy is received from the opposite pipe wall. If an echo is received, then the pipe is full of liquid at the point of attachment because the burst of energy was not greatly attenuated by the presence of air. If an echo is not received, the detector assumes that air is present since the energy burst was greatly attenuated.
The detector may generate an electronic window which controls the time during which the detector is responsive to the receipt of echoes. The purpose of the electronic window is to effectively filter out spurious echoes that are produced, for example, by travel of the burst of energy around the circumference of the pipe instead of directly through the pipe as intended. Such an electronic window would correspond generally to the time during which the detector expects an echo to be received from a point directly across the pipe.
A detector as described generally above is disclosed in U.S. Pat. No. 4,630,245 to Dam. While the operation of the Dam detector may be generally satisfactory, it suffers from the disadvantage that there is no easy manner in which to change the position of the electronic window to account for pipes of different sizes. In particular, the Dam detector uses a delay multivibrator that causes the position of the window to be predetermined. As a result, the Dam detector would require component changes to accommodate pipes of different diameters. Making such component changes would be tedious, time-consuming, and perhaps beyond the capability of operators in the field who may not be trained as electrical technicians.
Conventional ultrasonic detectors such as the Dam detector are also limited in their ability to accommodate various pipe sizes since they have no convenient manner of tuning them in the field, including adjusting the strength of the received echo signal or the frequency at which energy bursts are transmitted within the container.
U.S. Pat. No. 4,280,126 to White discloses a liquid level detector that determines whether liquid is present or absent at the point of attachment of the detector to a container. The detector utilizes an electronic window that is stated to be adjustable by a selector dial. A gain dial is adjusted to raise the amplitude at which the reception of reflected ultrasonic signals occurs. When the gain and selector dials are appropriately adjusted, an LED indicator is illuminated. However, there is no disclosure of the specific manner of operation of the White detector or that pipe size information is provided along with the selector dial.
According to one prior art detector tuning procedure, which was performed by the manufacturer of a detector, the detector was attached to a sample of pipe having the exact same dimensions and of the same material as the actual pipe to which the detector was to be eventually attached. The customer would typically provide the information about the pipe size and material to the manufacturer of the detector. The pipe sample was needed since the tuning of the detector was typically performed at a place other than the location of the actual pipe to which the detector was to be attached. This was necessary since such a conventional detector did not have any convenient manner of tuning it in the field.
During the tuning procedure, an oscilloscope or other electrical sensing device was attached to the detector, and the detector was tuned during operation in accordance with the visual display provided by the oscilloscope. The tuning included adjusting the frequency at which an energy burst was transmitted to increase and/or decrease the magnitude of the echo based on the visual display generated by the oscilloscope. The adjustment of the frequency was facilitated by a potentiometer.
The tuning procedure also included setting the magnitude of the echo signal received by the detector and setting the position of the window, based on the visual display provided by the oscilloscope. These two settings were accomplished by choosing and installing in the detector components, resistors for example, having certain specific values. These components were not installed in the detector prior to the tuning procedure. After the completion of tuning, the detector was then shipped to the customer and coupled to the actual pipe in the field for normal operation.
A significant problem occurred as a result of the tuning procedure described above. In a significant number of cases, the detector failed to operate properly when attached to the actual pipe in the field. It was discovered that one reason for this failure to operate was caused by material build-up on the interior of the pipe to which the detector was attached. The build-up of material on the interior of the pipe changed the transmission characteristics of the pipe. Another reason for the failure of the detector to operate properly was that the customer inadvertently provided erroneous information to the manufacturer concerning the actual pipe to which the detector was to be attached.
In either of the above cases, the detector had to be removed from the pipe, returned to the place where it was originally tuned, retuned, shipped back to the customer, and reattached to the actual pipe. Sometimes the detector was retuned in the field by the manufacturer's personnel with the use of an oscilloscope. The need to retune the detector was obviously cumbersome.